1. Field of the Invention
The present disclosure relates to a regenerative inverter device and an inverter device using a unit power cell, and more particularly, to a regenerative inverter device and an inverter device using a unit power cell capable of achieving the volume and cost reduction of a system through DC-link voltage pulsation improvement in a regenerative inverter device and an inverter device using a unit power cell.
2. Description of the Related Art
A high voltage inverter may denote an inverter having input power with a line-to-line voltage root-mean-square (RMS) value above 600 V. Such a high voltage inverter is mainly used in the application field such as a fan, a pump, a compressor or the like.
In a high voltage inverter used in the application field, a variable speed operation frequently occurs, and thus a regenerating operation using a regenerative inverter is used when fast acceleration or fast deceleration operation is required, thereby supporting fast acceleration or fast deceleration. Furthermore, for example, such a regenerating operation is essentially required for application fields such as traction, hoist, conveyor, and the like.
FIG. 1 illustrates a connection configuration of a typical high voltage inverter device.
There are various kinds of high voltage inverters, but for an example of a high voltage inverter driven by unit power, as illustrated in FIG. 1, the high voltage inverter 100 receives 3-phase power to replace the phase, and enhances the harmonic distortion ratio of the power current, and then generates unit power through a transformer, and synthesizes the unit power into a 3-phase voltage to supply it to a 3-phase motor according to each phase.
FIG. 2 illustrates a unit power cell configuration of the high voltage inverter 100.
Each unit power cell may include an inductor 202 for receiving AC power from an input power unit 201 to store and supply the power, a converter 203 for converting power passed through the inductor 202 to DC power, a converter controller 206 for controlling the converter 203, a capacitor 204 for absorbing the input/output power of the converter 203, an inverter 205 for converting the DC power to AC power again, and an inverter controller 207 for controlling the inverter 205.
A unit power cell included in the inverter device 100 receives single phase power to supply a phase voltage. The specific operation thereof is carried out according to the switching control of the converter controller 206 and inverter controller 207, and the detailed operation thereof may be described with reference to Chapter 7, Bin Wu, High-Power Converters and AC Drive, Wiley-Science.
More specifically, the converter controller 206 is an output port of the converter 203 to control a DC line voltage connected to the capacitor 204. In general, the capacitor 204 is used to resolve power imbalance in the input/output ports, and the DC line voltage is increased when input power supplied from the power source side is greater than output power consumed at the load, and the DC line voltage is decreased in the opposite case to perform an absorption operation. FIGS. 3 and 4 illustrate a DC line voltage controller configurations of the converter controller 206 for controlling a DC line voltage.
A typical DC line voltage controller may be selectively configured according to the application field in the form of an integral proportional controller as illustrated in FIG. 3 or an proportional integral controller as illustrated in FIG. 4.
In each drawing, Kp denotes a proportional gain, Ki denotes an integral gain, Vdc may represents a measurement value of a DC line voltage outputted to the capacitor 204, and Vdc* represents a DC line voltage control command signal value.
Based on a dq coordinate system current, a q-axis current command signal iq* acquired in FIG. 3 may be calculated as in Equation 1, and a q-axis current command signal iq* acquired in FIG. 4 may be calculated as in Equation 2.
                              i          q                      e            *                          =                                            -                              K                p                                      ⁢                          v              dc                                +                                    K              i                        ⁢                          ∫                                                (                                                            v                      dc                      *                                        -                                          v                      dc                                                        )                                ⁢                                  ⅆ                  t                                                              +                                                    P                ^                            out                                                      1                2                            ⁢              E                                                          [                  Equation          ⁢                                          ⁢          1                ]                                          i          q                      e            *                          =                                            K              p                        ⁡                          (                                                v                  dc                  *                                -                                  v                  dc                                            )                                +                                    K              i                        ⁢                          ∫                                                (                                                            v                      dc                      *                                        -                                          v                      dc                                                        )                                ⁢                                  ⅆ                  t                                                              +                                                    P                ^                            out                                                      1                2                            ⁢              E                                                          [                  Equation          ⁢                                          ⁢          2                ]            
As described above, the voltage of the capacitor 204 connected to a DC line may be controlled by a DC line voltage controller, and the output of the DC line voltage controller may be a q-axis current command signal (iq*). The current controller of the second portion 206 controls d, q-axis currents, respectively, in the synchronous coordinate system according to the current command signal, wherein the q-axis current component is referred to as an effective power current and d-axis current component is defined as an ineffective power current.
An AC power line power factor may be controlled according to the operation of the current controller of the second portion 206 when the need arises. When the power voltage and current are sinusoidal waves, the power factor (PF) may be expressed as follows.
                                                        PF              =                            ⁢                                                                    e                    dq                    e                                    ·                                      i                    dq                    e                                                                                                                                  e                      dq                      e                                                                            ⁢                                                                                i                      dq                      e                                                                                                                                                                  =                            ⁢                                                i                  q                  e                                                                                            i                      d                                              e                        2                                                              +                                          i                      q                                              e                        2                                                                                                                                                    [                  Equation          ⁢                                          ⁢          3                ]            
Here, edq^e=ed^e+jeq^e, idq^e=id^e+jiq^e, and edq^e·idq^e denotes an inner product of a power voltage complex vector and a current complex vector in the synchronous coordinate system, and |edq^e∥idq^e| may denote a product of each complex vector size. A synchronous coordinate system d-axis current command signal value id^e* for controlling a power factor output from the DC line voltage controller may be expressed as follows from Equation 3.
                              i          d                      e            *                          =                              i            q                          e              *                                ⁢                                                    1                -                                  PF                                      *                    2                                                                                      PF              *                                                          [                  Equation          ⁢                                          ⁢          4                ]            
On the other hand, the current controller of the second portion 206 may be configured as illustrated in FIG. 5. The current controller may output a voltage command signal using a proportional integral controller and a feed forward compensator according to a current command signal calculated through power factor control outputted from the foregoing DC line voltage controller and a current measured through the current sensor.
In FIG. 5, Kpd and Kpq may denote a proportional gain value to a d-axis current command signal and a proportional gain value to a q-axis current command signal, respectively, and Kid and Kiq may denote an integral value to a d-axis current command signal and an integral value to a q-axis current command signal, respectively.
A voltage command signal value outputted by the current controller in FIG. 5 is as follows.vqe*=Kp(iqe*−iqe)+Ki∫(iqe*−iqe)dt+vq—ffe*vde*=Kp(ide*−ide)+Ki∫(ide*−ide)dt+vd—ffe*vq—ffe*=−ωeLinteriqe vd—ffe*=ωeLinteride  [Equation 5]
The generated voltage command signal may be converted and output to a single phase stationary coordinate system to be used in the converter 203.
On the other hand, the voltage pulsation of a unit power cell including the second portion 206 can be obtained as follows.
First, the input voltage and current of the unit power cell may be expressed as Equation 6.vs(t)=√{square root over (2)}Vs sin(ωst)is(t)=√{square root over (2)}Is sin(ωst+δ)  [Equation 6]
In Equation 6, δ is a phase difference between the input voltage and current of the converter 203, and ωs is an input power frequency, t is a time, and Vs and Is are input voltage and current root-mean-square (RMS) values.
Furthermore, input power ps(t) obtained from Equation 6 is as follows.ps(t)=vs(t)is(t)=VsIs[cos(δ)−cos(2ωst+δ)]  [Equation 7]
In this case, the output voltage and current of each unit power cell may be defined as Equation 8.v0(t)=√{square root over (2)}V0 sin ωot i0(t)=√{square root over (2)}I0 sin(ωot+φ)  [Equation 8]
Here, φ may denote a load angle, ωo may denote an operating frequency, and t may denote a time. Furthermore, V0 and I0 may denote output voltage and current root-mean-square (RMS) values.
From Equation 8, the output power of the unit power cell may be computed as Equation 9.po(t)=v0(t)i0(t)=V0I0 cos φ−V0I0 cos(2ωot+φ)  [Equation 9]
As shown in Equation 9, it is seen that the input and output power of the unit power cell is comprised of a DC component and an AC component, and it is seen that the AC component of the input power has two times of the input frequency and the AC component of the output power has two times of the operating frequency.
Power transferred to the capacitor 204 connected to the DC line may be determined by a difference between the input power and output power of the converter 203. Furthermore, since the average values of the input power and output power should be the same, the remaining AC component may be power transferred to the capacitor 204. It may be expressed as Equation 10 below.pc=ps(t)−po(t)=VsIs cos(2ωst+δ)−V0I0 cos(2ωot+φ)  [Equation 10]
From Equation 10, it is seen that pulsations corresponding to two times of the input frequency and operating frequency are generated at the DC line, respectively, and it is seen that the pulsating size of the DC line power voltage is increased when the AC component of the input power and output power is increased.
Accordingly, pulsations corresponding to two times of the input line power frequency and output line operating frequency are generated in a large scale at the DC line voltage (capacitor 204 transfer voltage) of a power circuit comprised of the single phase converter 203 and inverter 205 of the unit power cell, and thus the capacitance of a DC line capacitor for reducing them may be required in a large scale. It increases the volume and cost of the entire system. Furthermore, the pulsation of the DC line voltage exerts an effect on the inverter output voltage, thereby reducing system reliability.